1. Field of the Invention
This invention relates to a fuel gas calorie control method and device for controlling the calories of a fuel gas (fuel gas produced using a blast furnace gas) which is supplied to blast furnace gas fired gas turbine equipment.
2. Description of the Related Art
An iron mill utilizes a blast furnace gas discharged from a blast furnace as a fuel gas for blast furnace gas fired gas turbine equipment, or utilizes it for other facilities to make the effective use of the blast furnace gas.
A blast furnace gas is a gas which is relatively low in calories, and always causes calorie changes, for example, depending on the operating state of a blast furnace. If a blast furnace gas is utilized as a fuel gas for blast furnace gas fired gas turbine equipment, therefore, a heat increasing gas is mixed with the blast furnace gas in order to produce a fuel gas utilizable for the blast furnace gas fired gas turbine equipment, and feedback on the calories of the mixed gas measured by a calorimeter is given to control the calories to a constant level. Moreover, advanced control is exercised such that the flow rate of the heat increasing gas mixed becomes a flow rate suitable for the flow rate of the gas turbine consumed fuel gas of the blast furnace gas fired gas turbine equipment.
This control will be explained further concretely based on FIG. 7. FIG. 7 is a configurational drawing of a conventional fuel gas production system. As shown in this drawing, a blast furnace gas and a heat increasing gas B (for example, a converter gas or a coke oven gas) are mixed in a first mixer 1, while a blast furnace gas and a heat increasing gas A (for example, a coke oven gas or a mixed gas consisting of a blast furnace gas and a coke oven gas) are mixed in a second mixer 2. A piping line 8 for supplying the heat increasing gas B to the mixer 1 is provided with a flow control valve 3 for the heat increasing gas B, and a shut-off valve 4 for the heat increasing gas B. On the other hand, a piping line 9 for supplying the heat increasing gas A to the mixer 2 is provided with a flow control valve 5 for the heat increasing gas A, and a shut-off valve 6 for the heat increasing gas A. The calories of a fuel gas to be supplied to blast furnace gas fired gas turbine equipment (i.e., the mixed gas consisting of the blast furnace gas and the heat increasing gas A, or the mixed gas consisting of the blast furnace gas and the heat increasing gas B) are measured by a fuel gas calorimeter 7 provided in a supply piping line 10 for the fuel gas. A conventional fuel gas calorie control device applied to this fuel gas production system exercises the following control:
(1) Advanced control is exercised on the assumption that the calories CALBF of the blast furnace gas, the calories CALmA of the heat increasing gas A, and the calories CALmB of the heat increasing gas B are constant. The amount of fuel gas consumption in the blast furnace gas fired gas turbine equipment varies according to the operating state of the gas turbine equipment (i.e., gas turbine output). Thus, the flow control valve 5 for the heat increasing gas A or the flow control valve 3 for the heat increasing gas B is operated in advance in response to a heat increasing gas requirement signal based on a gas turbine fuel gas requirement signal appropriate to the gas turbine consumed fuel gas flow rate.
(2) Only one of the heat increasing gas A and the heat increasing gas B is used (only one of the shut-off valves 4 and 6 is opened). Thus, CALt′=CALt always holds for the calories CALt′ of the mixed gas and the calories CALt of the fuel gas measured by the calorimeter 7.
(3) If discrepancy occurs in the advanced control owing to changes in the calories of the blast furnace gas, namely, if the calories CALt of the fuel gas measured by the calorimeter 7 differ from set calories (calories required by the blast furnace gas fired gas turbine equipment), the opening of the flow control valve 5 for the heat increasing gas A is controlled based on the deviation between the calories CALt of the fuel gas measured by the calorimeter 7 and the set calories to control the flow rate of the heat increasing gas A, or the opening of the flow control valve 3 for the heat increasing gas B is controlled based on the above deviation to control the flow rate of the heat increasing gas B, thereby bringing the calories CALt into agreement with the set calories (feedback control).
The following patent documents are available, for example, as prior art documents which disclose calorie control devices for a fuel gas (mixed gas):
Patent document 1 . . . Japanese Patent Application Laid-Open No. 2001-4132
Patent document 2 . . . Japanese Patent Application Laid-Open No. 1994-331131
The above-mentioned conventional fuel gas calorie control devices involved the following problems:
(1) Arbitrary mixing of the heat increasing gas into the blast furnace gas would contribute to calorie changes, and thus was not permissible.
(2) It was impossible to mix the two types of heat increasing gases A and B with the blast furnace gas at the same time and exercise control without interference.
(3) Since the calorimeter had a low response speed, the calorimeter was able to follow long-term (slow) calorie changes of the fuel gas (mixed gas), but was unable to follow short-term (rapid) calorie changes of the fuel gas (mixed gas) associated with changes in the flow rate of the heat increasing gas.
The present invention has been accomplished in light of the above-described circumstances. It is an object of the invention to provide a fuel gas calorie control method and device which can mix two types of heat increasing gases (first heat increasing gas, second heat increasing gas) into a blast furnace gas and exercise calorie control, can set the flow rate of the first heat increasing gas arbitrarily, can follow rapid calorie changes of a fuel gas (mixed gas) due to changes in the flow rate of the first heat increasing gas, and can further respond to calorie changes of the blast furnace gas, the first heat increasing gas, or the second heat increasing gas.